I want more bass in my 01 Box S. I'd also like to eliminate some of the existing distortion from bass heavy music (likely either by raising the high pass crossover point of the door woofers, or being able to EQ bass out with a sub doing the heavy lifting). I'll likely do other stereo upgrades in the future, but adding sub-bass seems like the area it lacks the most from the factory, as well as the the trickiest to solve given the space constraints in the 986 platform. I've researched several of the shallow subs available on the market and last night I pulled the trigger on one of these:
PHS.13 - Phantom - Subwoofers - Products
They are available for about $100 shipped, which seems like a good deal given the specs and design. They claimed at the time of release that was is the shallowest sub on the market at 2" mounting depth. Even the 8 and 10" shallow subs I was considering are deeper than the PPI (2.5" for the Pioneer 8" and 3 1/4 for the JL 10"). Rated at 200 watts, it's not going to win any Bass competitions, but I'm hopeful it will be able to cleanly fill the bottom end at a reasonable volume.
I will likely build an easy to remove, tall wedge box (5" or so deep at the bottom up the seat back to maybe 2" at the top yielding just over 1/2 cubic foot) with the driver firing into the passenger seat. The idea being I can pull it out to reclaim leg room when when I want to.
This specs say it can operate in a sealed enclosure as small as .5 cubic feet and designed for only .75 cubic feet. I might play with some box modeling software to see how ports might work too (with the idea of porting under the seat to take advantage of some additional cabin gain), however it's not designed or recommended for ported enclosures likely because the throw is so shallow.
I'll post updates here as the build progresses.
Has anyone else installed a shallow sub in your Box? I've seen a bunch of the footwell boxes, but they mostly seem to have standard depth/throw small subs in them.